The present invention relates to a shafting connection and, more particularly, to a shafting connection for connecting a first hollow steel shaft to a second hollow steel shaft, the shafts having identical outer diameters at least in regions extending from their abutting ends, comprising a friction coupling including an inner sleeve with an inner cylindrical surface arranged for frictional contact with the outer surface of the terminal region of the shafts, the friction coupling being arranged to be fitted on the aligned shafts to cover both shafts near their abutting ends, each of the shafts in a region extending from their abutting ends having a second concentric bore of same diameter for receiving an annular insert, said second bores being wider than the main shaft bores, the diameters of the second bores being essentially identical. Such connections are used, i.e., for the shafting of a controllable pitch propeller and similar devices.
Both solid and hollow marine shafts are usually connected to each other by means of press fit joints; see, e.g., published Swedish patent application No. 353 374 (application No. 8838/68). Such joints are sleeves which are fitted around the abutting cylindrical shaft ends, comprising inner and outer sleeve members with co-acting tapered surfaces. Hydraulic means are used for their assembly/disassembly. The torque transmission capacity of cylindrical shafts with or without cylindrical inner bores connected by press fit couplings solely depends on frictional force between the individual parts of the shafting assembly. Deformation of sleeve and shafts at high torque results in loss of friction and makes the shafts slip.
The transmission of high torque by hollow shafts shafted in this way constitutes a particular problem since hollow shafts are more easily deformed than solid shafts. To achieve torque transmission rates for hollow shafts comparable to those of solid shafts of same width, the former have to be reinforced by sleeves of toughened steel sunk into recesses turned beneath the coupling seatings, cf. "The OK couplings from OVAKO STEEL", brochure No. K1-189, page 13, OVAKO STEEL Coupings AB, 1988. For hollow shafts with an inner diameter/outer diameter ratio exceeding 0,55, even normal torque cannot be fully transmitted. Since a torque transmission safety factor against slipping of more than 2,5 of the normal torque is required by most marine classification authorities, specifications cannot be met with the known shafting connection even for shafts with that diameter ratio falling substantially below the 0,55 value. Furthermore, for a given application, it is desirable to decrease the shaft diameter while keeping maximum torque transmission values constant. In respect of shafts as such, this can be achieved by use of high quality alloyed steel. Such improvement however, is not parallelled by an increased efficiency of the now smaller press fit joint. Also for this reason, improvement of torque transmission efficiency of press fit joints is desirable.